1. Field of the Invention
The present invention relates to a dielectric resonator antenna mainly used in a microwave or millimeter wave region for a mobile communication, a satellite communication or a satellite broadcasting.
2. Description of the Related Art
Because a mobile communication, a satellite communication or a satellite broadcasting has been rapidly made progress, a transmit-receive device for the communication has been recently used in a house or automobile. In particular, because an antenna representing a radio terminal of the transmit-receive device is set up outside the house or a mobile station, it is required to downsize the antenna because of conditions for a set-up position and external appearance of the antenna.
Therefore, a resonance antenna is conventionally used as a downsized antenna. In the resonance antenna, a dielectric material having a relative dielectric constant higher than one is used to shorten a physical length of the resonance antenna and downsize the resonance antenna. For example, a microstrip antenna and a hemispherical dielectric resonator antenna are well-known. Because the hemispherical dielectric resonator antenna can be made by using a metal mold or the like and the number of etching steps required to make the hemispherical dielectric resonator antenna is small, the hemispherical dielectric resonator antenna can be easily mass-produced.
2.1. Previously Proposed Art
The hemispherical dielectric resonator antenna is, for example, disclosed in a literature "Theory and Experiment of a Coaxial Probe Fed Hemispherical Dielectric Resonator Antenna" IEEE Transactions on Antennas and propagation, Vol.41, No.10, pp.1390-1398, October 1993.
FIG. 1A is an oblique view of a conventional hemispherical dielectric resonator antenna disclosed in the above literature, and FIG. 1B is a cross sectional view of a hemispherical dielectric resonator shown in FIG. 1A.
As shown in FIGS. 1A and 1B, a hemispherical dielectric resonator 301 filled with a dielectric material is disposed on a ground plane 302, a coaxial probe 303 is tightly inserted in the hemispherical dielectric resonator 301 from a rear surface of the resonator 301 through a coaxial aperture 304 to fix the hemispherical dielectric resonator 301 on the ground plane 302. The coaxial probe 303 is located at a displacement b from the center of the hemispherical dielectric resonator 301. When a signal transmitting through the coaxial probe 303 is fed in the hemispherical dielectric resonator 301, the resonator 301 is resonated, and a linearly polarized wave having a fixed frequency is radiated from the resonator 301.
2.2. Problems to be Solved by the Invention
However, in the conventional hemispherical dielectric resonator antenna, it is required to feed the signal from a rear surface of the resonator 301 to the resonator 301 through the coaxial aperture 304. Therefore, there is a first drawback that it is difficult to arrange the hemispherical dielectric resonator 301 and the coaxial probe 303 on the same plane and a resonance frequency of the conventional hemispherical dielectric resonator antenna cannot be adjusted.
Also, in the conventional hemispherical dielectric resonator antenna, because the coaxial probe 303 is only inserted in the hemispherical dielectric resonator 301 to fix the hemispherical dielectric resonator 301 on the ground plane 302, there is a second drawback that the connection of the resonator 301 and the ground plane 302 is not sufficient and the resonator 301 easily comes off the grand plane 302. Also, because it is difficult to form an array antenna by setting a plurality of hemispherical dielectric resonator antennas in array, the adjustment of antenna characteristics in the array antenna cannot be performed.
Also, in cases where a positional relationship between a mobile body and a base station changes with the passage of time, an optimum antenna angle changes with the passage of time in the linearly polarized wave, and a wave receiving sensitivity is degraded in the conventional hemispherical dielectric resonator antenna. To perform a mobile communication, there is a case that a circularly polarized wave is utilized in the satellite broadcasting or the satellite communication in place of the linearly polarized wave. However, there is a third drawback that the linearly polarized wave is only used in the conventional hemispherical dielectric resonator antenna and the conventional hemispherical dielectric resonator antenna has no operational function for the circularly polarized wave.